There's a facebook virus / spyware that can cause your FaceBook to run slow, or show only white pages, or not load pages at all. To remove it, or to see if you have it:

• Click on your 'application settings'
• Click the dropdown box to show 'added to profile'
• If you see one in there named "un named app" delete it (Click the X to the right) ... Its an internal spybot.

• Go to your profile page, find any box on it
• Click on the "pencil" in the upper right-hand corner of the box
• Click "move to boxes tab"
• The "Boxes" tab will be back with all your goodies in it just like before.
• If you want the box you clicked on to get the "Boxes" tab back on your regular profile tab, just reverse the process just for that one box. (Choose "Move to wall tab")

By the way, the unnamed app will also show again in your application settings.
There is another possible Facebook Malware however. For more on that, see this thread.